Power electronic systems commonly employ one or more power electronic regulators that utilize power devices controlled by integrated circuits. The regulator is the basic module of the power electronic system. In general, a power electronic regulator controls and shapes an electrical input with a known magnitude and frequency into an electrical output with a different magnitude and frequency. The power flow through the regulators may be reversible, thus interchanging the roles of input and output. Specifically, DC/DC regulators convert one DC voltage level into another. In an AC/DC conversion, a given AC voltage is rectified and transformed into a desired DC voltage level.
There are many ways to classify regulators used in power electronics. These include classification by type of device used, function of the regulator, how the switching device in the regulator is switched and so on. Unfortunately, no well-defined categories based on these criteria are possible because of numerous exceptions to the standards.
One common regulator configuration is known as a linear regulator. These types of regulators linearly manipulate a given input voltage to produce a desired output voltage. In essence, such regulators can be simplistically modeled as a variable scaling resistor across which a portion of the input voltage is dissipated. The remaining voltage is then usable at the regulator output.
Another configuration is called a switching or switched-mode regulator. These regulators contain controllable switches which are turned on and off at frequencies that are high compared to a line frequency. By way of the switches, the regulator will deliver the full input voltage to the output for a period less than the entire duty cycle of the switches. An example of such a regulator could require a 5V output to be derived from a 10V input voltage. For a duty cycle equaling 1 .mu.sec, the switches may be switched to deliver the full 10V for half of the time, 0.5 .mu.sec. Thus if 10V is applied for half of the 1 .mu.sec period, the voltage for the entire period would be 5V. Then by employing a smoothing network, commonly a conventional LC circuit, the output is smoothed to an overall 5V output for the entire period.
Typical regulators produce an output voltage in a specified regulated range. This range or region is usually defined as the specific output voltage plus or minus a tolerable range voltage.
In the past, when a load was coupled to a regulator, a drop in the regulator's output voltage would result, commonly forcing that output voltage outside of its predetermined regulated range. Not only was this drop unacceptable since it deprived the load of necessary voltage, it could also result in malfunction of the load circuitry.
To combat this problem, designers began employing a system for positioning the output voltage of the regulator within a given operating range (commonly referred to as voltage positioning) in such a fashion as to compensate for the drop encountered when a load was brought online. Additionally, voltage positioning also must counteract disturbances encountered such as input voltage fluctuations, load current changes, switching ripples, stray transients, and variations in components tolerances or temperatures. Thus, the goal would be to position the output voltage at its highest range value at no load and lowest range value at maximum load.
Initially the solution to this problem entailed anticipating the connection of the load and calculating the associated voltage drop of the regulator output. Once estimated, the regulator output voltage would be adjusted to a higher output voltage such that when the load is coupled thereto and the resulting voltage drop occurs, the output voltage is still within the regulated range.
Determining how to adjust the regulator output voltage to operate within the imposed limits posed the primary problem in this system. Usually, a designer, assuming a constant output load and known internal regulator voltages, can devise a circuit which operates with set voltage limits. Known internal voltages can be calculated for known values as functions of the output load voltages. Thus, simple existing circuits are designed by employing simple static elements that increase the duty cycle of the regulator during given times.
Unfortunately, in practice, it has been found that the assumption of a fixed load is not entirely correct. While acceptable as a first attempt, such assumptions did not cover the full range of voltage responses from the load. In reality, load output voltages are not entirely fixed. Even in loads which have a known stable output voltage, the actual voltage characteristic may contain some variation due to unanticipated impedances.
Accordingly, what is needed in the art is a system and method of driving the output of the regulator as a function of the actual output voltage.